1. Field of the Invention
The present invention relates generally to a sample handling plate used for analyzing very small amounts of various samples (e.g., micro vital substances such as viruses and bacteria, vital formations such as cells and biopolymers, organic compounds other than biopolymers, inorganic substances and inorganic compounds). More specifically, the invention relates to a sample handling plate of a plastic, glass or the like, which is capable of being used for simultaneously examining the functions of a large number of genes and which is also capable of being used as a reactor in the PCR method for amplifying DNAs.
2. Description of the Prior Art
In recent years, of various methods for examining the functions of genes, the micro array technique capable of simultaneously examining thousands kinds to tens of thousands kinds of genes has been particularly noticed in the field of genome medical science and biochemistry.
In such a technical background, as shown in FIG. 24, there has been proposed an apparatus for holding small volumes of liquids, wherein a large number of substantially pyramidal minute wells (recessed portions) 101 are formed in a single flat plate 100 and wherein various liquid samples to be analyzed can be injected into the wells 101 to be simultaneously analyzed (see, e.g., U.S. Pat. No. 6,027,695).
As shown in FIG. 25, there has been also proposed a technique for forming a large number of protrusions 103 on the surface of a plate 102 to hold culture tissues or samples to be analyzed on the top faces 104 of the protrusions 103 (see Japanese Patent Laid-Open Nos. 7-115958 and 2003-4742).
As shown in FIG. 26, there has been also proposed an electrophoresis chip wherein fine grooves (recessed portions) 105 for moving a sample due to electrophoresis are formed in the surface 107 of a plate 106 for separating and extracting a chargeable substance (see, e.g., Japanese Patent Laid-Open No. 2000-310613).
In addition, there has been proposed a technique wherein a large number of samples are allowed to adhere to the surface of a flat plate at dense scattered points (see, e.g., Japanese Patent Laid-Open No. 2003-130879).
Moreover, as shown in FIG. 27, there has been proposed a plastic plate 108 which is capable of being used for carrying out tissue culture and immune analysis and which is capable of being used for many purposes, such as observation of morphology, measurement of absorbance, and measurement of fluorescence and fermentation. This plastic plate 108 is a plate of a transparent resin having a thickness of 0.5 mm or less and having a large number of wells 110 for housing therein a sample, and the plastic plate 108 is held in a holder 111 having a thickness of 1.0 mm or more (see Japanese Patent Laid-Open No. 2001-17155).
However, in the plates 100 and 102 disclosed in U.S. Pat. No. 6,027,695 and Japanese Patent Laid-Open Nos. 7-115958 and 2003-4742, the shape of the surface having the large number of wells (recessed portions) 101 or protrusions 103 is quite different from the shape of the reverse having no wells 101 or protrusions 103. Therefore, if the plate 100 or 102 is formed by the injection molding, the shrinkage percentage on the side of the surface is different from that on the side of the reverse during the injection molding, so that there are some cases where the resin plate 100 or 102 may warp as shown in FIG. 28.
If the plate 106 disclosed in Japanese Patent Laid-Open Nos. 2000-310613 and 2003-130879 is formed of a resin material, there are some cases where the plate 106 may warp due to the temperature difference between the surface and reverse sides since there are some cases where the plate 106 may be heated for promoting hybridization or the like (see FIG. 28).
When the plate 100, 102 or 106 thus warps, if a sample is measured by an optical measuring unit having a narrow focal point using laser beams or the like, the position of the focal point is displaced, so that there is the possibility that the precision of measurement deteriorates. Furthermore, as measures to prevent the warpage of the plates 100 and 102 disclosed in U.S. Pat. No. 6,027,695 and Japanese Patent Laid-Open Nos. 7-115958 and 2003-4742, it is effective to form a plate having a constant thickness as the plastic plate 108 disclosed in Japanese Patent Laid-Open No. 2001-17155. However, the technique disclosed in Japanese Patent Laid-Open No. 2001-17155 is directed to the plastic plate 108 wherein the volume of each well 110 is about one hundred microliters, so that the technique can not be used for forming such a small plate that the volume of each well 110 is about tens nanoliters. That is, if wells 110 having a very small volume of about tens nanoliters are densely formed, it is difficult to form the plastic plate 108 by the injection molding so that the plate 108 has a constant thickness.
Furthermore, if a plate of a material, such as a glass, other than plastics is used as a sample handling plate, the same warpage of the plate as that of a plastic plate may be caused. Therefore, it is desired to take measures to prevent such warpage.